The present invention relates to an apparatus for processing liquids such as water and the like by reverse osmosis.
In the art of processing liquids, it has been already proposed to use a reverse osmosis device for desalinization and decoloration of drinking water, industrial water or waste water as well as for upgrading of aqueous solutions and of waste waters in order to remove noxious matters. Furthermore, the reverse osmosis is employed in the recovering of metals during the concentrating of solutions.
Reverse osmosis is the transmuted natural principle of the osmosis utilized for technical applications.
In the osmosis, the equalization of different concentrations of solution occurs through semi-permeable membranes. The solution pressure of different concentrations is designated as osmotic pressure by which the water molecules try to dilute the concentrated solution. The osmotic process is terminated when an equilibrium is obtained.
In opposition to this, the reverse osmosis tries to counteract the dilution of the concentrating phase in order to achieve a further concentration wherein a higher pressure must be used than the present osmotic pressure. In this case, the semi-permeable membrane acts as a carrier for all dissolved substances so that a pure liquid the permeate is obtained at the outlet.
The pressure required for the reverse osmosis is produced by increasing the pressure, for example, by interposing a pump ahead of the reverse osmosis device. Although this principle seems to be sound, there is the disadvantage of a rather remarkable loss of energy since the pressure of the concentrate discharge is not utilized any more and therefore gets lost. This, however, undesirably increases the expenses of the apparatus.
The German specification DE-OS No. 2547446 describes method for purification of waste water solutions wherein the pressure energy in the concentrate is recovered by expanding the concentrate in a turbine which is directly connected to a pump. The disadvantage of the specification is, however, that the recovered energy is not sufficient to maintain or provide the required pressure for the solution to be treated when entering the reverse osmosis unit. Thus, the pump must be continuously in operation.